A technique has conventionally been known that an electric current is detected using one shunt resistance inserted into a direct-current part of an inverter circuit when U-, V- and W-phase currents are detected for the purpose of controlling an electric motor. In order that all the three-phase currents may be detected in the above-mentioned manner, a three-phase PWM (pulse width modulation) signal pattern needs to be generated in one period of a PWM carrier so that two or more phase currents can be detected. For this purpose, a motor control device has been conventionally proposed which can normally detect two or more phase currents by shifting a phase of the PWM signal in one period, without increase in noise. See Japanese Patent No. 5178799, the contents of which are incorporated herein by reference.
Further, the PWM control of the three-phase motor includes a three-phase modulation manner and a two-phase modulation manner. The three-phase modulation manner increases switching loss in an inverter circuit. Hence, some products use the two-phase modulation manner with emphasis on reducing switching loss. However, when the above-described conventional current detection manner is applied to the two-phase modulation, there results in a problem that only one phase current can be detected in two occurrences of current detection timing in a region where a modulation factor is increased.